Copolymer for semiconductor lithography and producing method thereof, and composition

ABSTRACT

In order to improve a resist pattern shape in a semiconductor lithography process, which is a factor largely affecting on a processing precision, an integration degree and yield, a copolymer for semiconductor lithography where a composition of a hydroxyl group-containing repeating unit in a low molecular weight region is controlled, and a method of producing the same are provided. 
     According to the invention, in a copolymer for semiconductor lithography, which is obtained by copolymerizing a monomer having a hydroxyl group and a monomer having no hydroxyl group, when a copolymer of which composition of a hydroxyl group-containing repeating unit is controlled is used, the object can be achieved.

TECHNICAL FIELD

The present invention relates to a copolymer suitable for forming acoating film, such as a resist film used in a semiconductor lithographyprocess, an anti-reflective film or the underlayer film of amulti-layered resist, to a method for the production thereof, and to acomposition containing said copolymer for a semiconductor lithography.

BACKGROUND ART

In a lithography process employed for producing a semiconductor,formation of a finer pattern is increasingly required so as to matchwith an elevated degree of integration. For formation of a finerpattern, it is essential that the length of the light wave beaming froman exposure light source be made as shorter as possible. At present, alithography using a krypton fluoride (KrF) excimer laser (wavelength:248 nm) is becoming mainstream, and a lithography using an argonfluoride (ArF) excimer laser (wavelength: 193 nm), which enables a linewidth of 100 nm or less, is expected to come into practical use.Furthermore, various kinds of radiation lithography technologies using ashort wavelength, such as fluorine dimer (F₂) excimer laser light(wavelength: 157 nm), extreme-UV rays, X-rays or electron beams, are ina developmental stage.

In semiconductor lithography processes, in a resist film where by makinguse of a variation of the solubility to an alkali developer under anaction of acid, a resist pattern for transferring on a substrate isformed, and in an upper layer of the resist film or a lower layer of theresist film, various kinds of coating films are used. It can be citedthat as a coating film applied to, for instance, a lower layer, that is,as a lower layer film, an anti-reflective film that suppresses lightfrom being reflected from a substrate to accurately form a fine resistpattern, a flattening film that is used in a lower layer of a resist tomake irregularity formed on a surface of the substrate flat when aresist pattern is further formed on the substrate thereon a pattern isformed, and an underlayer film or the like in a multi-layered resistthat is used to transfer a resist pattern owing to dry etching.

These coating films can be formed in such a manner that a coatingsolution where a copolymer for lithography, which has a function of eachof the coating films, other additives are dissolved in an organicsolvent is prepared, the coating solution is coated on a substrateaccording to a method such as a spin coating method, and as needs arisethe solvent is removed by heating or the like. In a copolymer used forlithography at that time, in addition to the optical properties that aredemanded for a resist film and an anti-reflective film, chemicalproperties, coating properties and physical properties such as theadhesiveness to the substrate or the lower layer film, a fundamentalproperty as a coating copolymer such that foreign matters that disturbthe formation of a fine pattern are not present is demanded.

As a resist copolymer that is a copolymer used in a resist film, thereare a negative type copolymer in which owing to an action of acid thesolubility to an alkali developer is decreased and a positive typecopolymer in which owing to an action of acid the solubility to analkali developer is increased. The positive type resist copolymer isconstituted necessarily including a repeating unit having a polar groupthat improves the adhesiveness to a semiconductor substrate and anunderlayer film, or controls the solubility to a lithography organicsolvent or an alkali developer and a repeating unit having a structurewhere a nonpolar substituent group is dissociated by acid to develop apolar group soluble in an alkali developer, and, as needs arise, arepeating unit having an acid-stable nonpolar substituent group forcontrolling the solubility to the lithography organic solvent and thealkali developer.

Specific examples of such a positive type resist copolymer include, inthe KrF lithography process, a copolymer that includes a repeating unitderived from hydroxystyrene and a repeating unit derived fromacid-decomposable alkoxystyrene; a copolymer that includes a repeatingunit derived from hydroxystyrene and a repeating unit derived from anacid-decomposable alkyl (meth) acrylate; and a polymer wherein thehydroxystyrene-derived repeating unit has been partially protected withan acetal are known. In the ArF lithography process, a copolymer or thelike that includes a repeating unit derived from (meth)acrylatesubstituted by a hydroxyalkyl group and a repeating unit derived fromacid-decomposable alkyl (meth)acrylate is known.

A repeating unit that has a hydroxyl group is readily dissolved in analkali developer. Accordingly, when the repeating unit that has ahydroxyl group is used as for instance a resist film, a resist patterncan be appropriately smoothed and the roughness can be suppressed lowand so on. Furthermore, the solubility to the alkali developer isdifferent depending on a molecular weight of a copolymer as well. Thatis, in general, the larger the molecular weight thereof is, the smallerthe solubility thereof is, and the smaller the molecular weight thereofis, the larger the solubility thereof is. Accordingly, the higher acomposition of a repeating unit that is small in the molecular weightand has the hydroxyl group is, the larger the solubility to the alkalideveloper is. In general, when a copolymer is designed, by taking such anature into consideration, a composition of the repeating unit having ahydroxyl group and a molecular weight thereof are designed. Normally, acopolymer has a molecular weight distribution, and a composition of thepolymer is different between a high molecular weight component and a lowmolecular weight component (hereinafter, referred to as “composition ina molecular weight direction”). Thus, when a composition of a hydroxylgroup is different in a molecular weight direction, a pattern asdesigned cannot be depicted. For instance, when a repeating unit thatcontains a hydroxyl group in a low molecular weight region is containedmuch, a top shape of a pattern tends to be rounded, by contrast, whenthe repeating unit that contains a hydroxyl group in a low molecularweight region is contained less, the top shape of a pattern tends to beangulated or rougher. Such a problem is becoming incapable of neglectingas a pattern becomes finer.

As a copolymer of which composition in a molecular weight direction iscontrolled, an example that is a copolymer containing an alicyclicstructure and a lactone structure, in which a lactone composition in amolecular weight direction is controlled within ±10%, is known (patentliterature 1). Furthermore, an example that is a copolymer between amonomer having an alicyclic structure and p-acetoxystyrene, in which ap-acetoxystyrene composition in a molecular weight direction iscontrolled within ±10%, is known (patent literature 2). The technologieseach have proposed a method where, in a two-component copolymer that hasan alicyclic structure and a lactone structure or a monomer having analicyclic structure and p-acetoxystyrene, in order to improve thesolubility to a solvent, a lactone or p-acetoxystyrene composition iscontrolled.

As a similar technology, a technology where a monomer having a polargroup such as a hydroxyl group and a monomer not containing a polargroup are supplied in a heated polymerization solvent together with apolymerization initiator and a polymerization catalyst to polymerize isknown (patent literatures 3 and 4). The technology has proposed, inorder to improve the adhesiveness with a substrate, a method ofpolymerizing a monomer having a polar group-containing alicyclicfunctional group. However, in all of the above-described technologies,the relationship between a composition control in a low molecular weightregion and the lithography characteristics is not disclosed.

In a polymerization solution after a polymerization reaction, other thana copolymer, there are low molecular weight impurities such as anunreacted monomer and impurities derived from the polymerizationinitiator or the polymerization catalyst. The low molecular weightimpurities are unfavorable because, in the semiconductor lithographyprocess, the impurities volatilize to stick to an optical system of anexposure device, generate a defect in a pattern or cause a variation inthe nature of the copolymer during storage. In this connection, a methodis known where a polymerization solution is mixed with a poor solvent toprecipitate a copolymer as a solid content (hereinafter, referred to as“reprecipitation”) or a precipitated copolymer is washed with a poorsolvent (hereinafter referred to as “washing”), and thereby thecopolymer is refined (hereinafter referred to “refining”) owing tosolubility difference to the poor solvent of the copolymer and the lowmolecular weight impurities. The refining process is applied in almostall of the above referenced literatures. Other than the above, a methodwhere a composition of the solvent is controlled so that a residualmonomer may be 5% or less (patent literature 5), a method where acopolymer-containing slurry dispersed in a solvent is heated (patentliteratures 6 and 7) and a method where, by use of a poor solvent,reprecipitation or rinse is applied to remove an insoluble content toimprove the solvent solubility (patent literature 8) or the like areknown.

However, in all of the technologies, the poor solvent that is broughtinto contact with the copolymer is, in each of reprecipitation and/orwashing step, only a polar solvent having a hydroxyl group or only anonpolar solvent that does not have a hydroxyl group. In the refiningstep, since the solubility difference between a low molecular weightregion of the copolymer and the low molecular weight impurities to beremoved is small, the low molecular weight region of the copolymer ispartially removed. Accordingly, there are problems in that, when a polarsolvent having a hydroxyl group is used to refine, a composition of ahydroxyl group-containing repeating unit in the low molecular weightregion of the polymer is lowered, and when a nonpolar solvent is used torefine, a composition of a hydroxyl group-containing repeating unit inthe low molecular weight region of the polymer is raised.

From these backgrounds, in a copolymer for semiconductor lithography,which is obtained by copolymerizing a monomer having a hydroxyl groupand a monomer that does not have a hydroxyl group, only a polymer wherea composition of a hydroxyl group-containing repeating unit in the lowmolecular weight region is deviated from an average composition isknown. Accordingly, a problem relating to a shape of a lithographypattern such as mentioned above is not yet overcome.

Patent literature 1: WO99/50322

Patent literature 2: JP-A 2001-151823

Patent literature 3: JP-A 2002-194029

Patent literature 4: JP-A 2003-306514

Patent literature 5: JP-A 2001-109153

Patent literature 6: JP-A 2002-201210

Patent literature 7: JP-A 2002-229220

Patent literature 8: JP-A 2003-213721

DISCLOSURE OF INVENTION Problem that the Invention is to Solve

The object of the present invention is to provide a copolymer forsemiconductor lithography where in order to improve a resist patternshape in a semiconductor lithography process, which is a large factorthat largely affects on processing accuracy to determine an integrationdegree and a yield, a composition of a hydroxyl group-containingrepeating unit in a low molecular weight region is controlled, and aproducing method thereof.

Means for Solving the Problem

The present inventors, after studying hard, found that, in a copolymerfor semiconductor lithography, which is obtained by copolymerizing amonomer having a hydroxyl group and a monomer having no hydroxyl group,when a copolymer is used where a molar composition of a hydroxylgroup-containing repeating unit in a low molecular weight region iscontrolled, the above object can be achieved, and thereby the inventioncame to completion. In general, a kind of a copolymer, an averagecomposition and an average molecular weight are controlled to control apattern shape. However, it was found by the invention that, when onlythe above-mentioned factors are controlled, a pattern shape as designedcould not be obtained. That is, when a composition of a hydroxyl groupin a molecular weight direction is controlled, a pattern as designed,which can respond to a demand for miniaturization, can be formed.

That is, the invention, in a copolymer for semiconductor lithography,which is obtained by copolymerizing a monomer having a hydroxyl groupand a monomer having no hydroxyl group, provides a copolymer forsemiconductor lithography where a molar composition of a hydroxylgroup-containing repeating unit in a low molecular weight regioncorresponding to 5% of a copolymer total peak in gel permeationchromatography is within ±10% of an average molar composition of thehydroxyl group-containing repeating unit in a total copolymer and acomposition for semiconductor lithography, which contains the copolymer.

Furthermore, the invention provides a producing method of a copolymerfor semiconductor lithography, in which a copolymer for semiconductorlithography, which is obtained by copolymerizing a monomer having ahydroxyl group and a monomer having no hydroxyl group, is obtained byundergoing, after a polymerization reaction, a step of bringing anobtained copolymer into contact with a polar solvent having a hydroxylgroup to reprecipitate or wash; and a step of bringing the obtainedcopolymer into contact with a nonpolar solvent having no hydroxyl groupto reprecipitate or wash.

ADVANTAGE OF THE INVENTION

According to the invention, with a copolymer in which a composition of ahydroxyl group-containing repeating unit of a low molecular weightregion, which largely affects particularly on a pattern shape, iscontrolled, a fine pattern excellent in the rectangularity can be formedand thereby a dense and fine integrated circuit can be formed.

BEST MODE FOR CARRYING OUT THE INVENTION

A copolymer for semiconductor lithography according to the inventionnecessarily includes, in order to improve the adhesiveness with asemiconductor substrate or an underlayer film and to control thesolubility to a lithography organic solvent or an alkali developer, atleast a hydroxyl group-containing repeating unit. Furthermore, thecopolymer for semiconductor lithography according to the invention isconstituted including a repeating unit that does not contain a hydroxylgroup, which has functions necessary for a resist layer, an underlayerfilm of a multi-layer resist, an anti-reflection film and so on.Accordingly, the copolymer for semiconductor lithography according tothe invention can be obtained by copolymerizing at least one kind of amonomer having a hydroxyl group and at least one kind of a monomerhaving no hydroxyl group.

When the copolymer is used in a positive type resist, the copolymernecessarily includes, at least, a hydroxyl group-containing repeatingunit (A) that improves the adhesiveness with a semiconductor substrateor an underlayer film or controls the solubility to a lithographyorganic solvent or an alkali developer; a repeating unit (B) that has astructure where a substituent group having no hydroxyl group isdissociated by acid to develop a polar group soluble in an alkalideveloper; and, as needs arise, a repeating unit (C) having a polargroup other than a hydroxyl group or an acid-stable repeating unit (D)not having a polar group such as a hydroxyl group to control theadhesiveness and the solubility.

The hydroxyl group-containing repeating unit (A) that controls theadhesiveness or the solubility can be introduced by copolymerizing amonomer having a hydroxyl group. As such monomers, for instance,compounds having a phenolic hydroxyl group, an alcoholic hydroxyl group,a carboxyl group, a hydroxyhalogenoalkyl group or the like can be cited.Specifically, 1) hydroxystyrenes, 2) hydroxyhalogenoalkyl styrenes, 3)carboxylic acids having an ethylenic double bond, 4) hydroxylkyl estersof 3), 5) hydroxyhalogenoalkyl esters of 3) and so on can be cited.Here, as an alkyl group in a hydroxyalkyl or hydroxyhalogenoalkylportion in 2), 4) and 5), a linear, branched or cyclic alkyl grouphaving 1 to 20 carbon atoms can be cited. Furthermore, as a halogenogroup, a fluoro group, a chloro group or a bromo group can be cited.Still furthermore, as a carboxylic acid having an ethylenic double bond,(meth)acrylic acid is preferable.

Specific examples of such monomer include 1) hydroxystyrenes such asp-hydroxystyrene, m-hydroxystyrene, p-hydroxy-α-methylstyrene and so on;2) hydroxyhalogenoalkylstyrenes such asp-(2-hydroxy-1,1,1,3,3,3-hexafluoro-2-propyl)styrene and so on; 3)carboxylic acids having an ethylenic double bond such as acrylic acid,methacrylic acid, maleic acid, fumaric acid, α-trifluoromethylacrylicacid, 5-norbornene-2-carboxylic acid,2-trifluoromethyl-5-norbornene-2-carboxylic acid,carboxytetracyclo[4.4.0.1^(2,5).1^(7,10)]dodecyl methacrylate and so on;4) hydroxyalkylesters where a carboxyl group of carboxylic acid havingan ethylenic double bond is substituted by a hydroxyalkyl group such asa hydroxymethyl group, a hydroxyethyl group, a hydroxypropyl group, ahydroxy-8-tricyclo[5.2.1.0^(2,6)]decanyl group, a 3-hydroxy-1-adamantylgroup or the like; and 5) hydroxyhalogenoalkyl esters where a carboxylicgroup of carboxylic acid having an ethylenic double bond is substitutedby a (2-hydroxy-1,1,1,3,3,3-hexafluoro-2-propyl)methyl group, a5-(2-hydroxy-1,1,1,3,3,3-hexafluoro-2-propyl)methyl-2-norbornyl group, a5-(2-hydroxy-1,1,1,3,3,3-hexafluoro-2-propyl)methyl-3-norbornyl group, a5-(2-hydroxy-1,1,1,3,3,3-hexafluoro-2-propyl)-2-norbornyl group, a2-(4-(2-hydroxy-1,1,1,3,3,3-hexafluoro-2-propyl)cyclohexyl)-1,1,1,3,3,3-hexafluoropropylgroup and so on.

The repeating unit (B) that has a structure where a substituent grouphaving no hydroxyl group is dissociated by acid to develop a polar groupsoluble in an alkali developer can be obtained by polymerizing a monomerhaving a structure that is decomposed by acid to be alkali soluble or,after a monomer having an alkali soluble structure is polymerized, byprotecting the alkali soluble group with a group (acid dissociativegroup) that is not dissolved in alkali but is dissociated by acid.

As acid dissociative group having no hydroxyl group, saturatedhydrocarbon groups such as a tert-butyl group, a tert-amyl group, a1-methyl-1-cyclopentyl group, a 1-ethyl-1-cyclopentyl group, a1-methyl-1-cyclohexyl group, a 1-ethyl-1-cyclohexyl group, a2-methyl-2-adamantyl group, a 2-ethyl-2-adamantyl group, a2-propyl-2-adamantyl group, a 2-(1-adamantyl)-2-propyl group, a8-methyl-8-tricyclo[5.2.1.0^(2,6)]decanyl group, a8-ethyl-8-tricyclo[5.2.1.0^(2,6)]decanyl group, a8-methyl-8-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodecanyl group, a8-ethyl-8-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodecanyl group and thelike; and oxygen-containing hydrocarbon groups such as a 1-methoxyethylgroup, a 1-ethoxyethyl group, a 1-iso-propoxyethyl group, a1-n-butoxyethyl group, a 1-tert-butoxyethyl group, a1-cyclopentyloxyethyl group, a 1-cyclohexyloxyethyl group, a1-tricyclo[5.2.1.0^(2,6)]decanyloxyethyl group, a methoxymethyl group, aethoxymethyl group, an iso-propoxymethyl group, a n-butoxymethyl group,a tert-butoxymethyl group, a cyclopentyloxymethyl group, acyclohexyloxymethyl group, a tricyclo[5.2.1.0^(2,6)]decanyloxymethylgroup, a tetrahydropyranyl group, a tert-butoxycarbonyl group and thelike can be cited. Here, as a saturated hydrocarbon group, a linear,branched or an alicyclic hydrocarbon group having 1 to 20 carbon atomsis preferable. Furthermore, as an oxygen-containing hydrocarbon group, alinear, branched or an alicyclic hydrocarbon group having an ether bondor an ester bond having 2 to 24 carbon atoms in total.

As a monomer that has an acid dissociative group, a compound where ahydroxyl group of a compound shown in for instance (A) is protected withan acid dissociative group that does not have the hydroxyl group or thelike can be cited. Furthermore, when after a monomer having an alkalisoluble group that is not protected is polymerized, the alkali solublegroup is protected with an alkali insoluble acid dissociative group, themonomer having the alkali soluble group is polymerized as it is,followed by, in the presence of an acid catalyst, reacting with acompound that gives rise to an alkali-insoluble substituent group suchas vinyl ether or halogenated alkyl ether. As an acid catalyst that isused in a reaction, p-toluene sulfonic acid, trifluoroacetic acid, astrong acidic ion exchange resin and so on can be cited.

The repeating unit (C) having a polar group other than a hydroxyl groupfor controlling the adhesiveness and the solubility can be introduced bycopolymerizing a monomer having a polar group other than a hydroxylgroup. As an example of such a monomer, a compound where a hydroxylgroup of a monomer having a hydroxyl group exemplified in (A) issubstituted by a substitution group having a polar structure such as, inaddition to maleic anhydride and maleimide, lactone, acid anhydride,imide, nitrile, carbonate or the like can be cited. A particularlypreferable polar substituent group is a substituent group containing alactone structure. Examples of substituent group having a lactonestructure include substituent groups containing a lactone structurehaving 4 to 20 carbon atoms in total such as γ-butyrolactone,γ-valerolactone, δ-valerolactone, 1,3-cyclohexane carbolactone,2,6-norbornane carbolactone, 4-oxatricyclo[5.2.1.0^(2,6)]decane-3-one,mevaloic acid δ-lactone and so on, and ester compounds where by thesubstituent group a carboxyl group of carboxylic acids having anethylenic double bond such as acrylic acid, methacrylic acid, maleicacid, fumaric acid, α-trifluoromethyl acrylic acid,5-norbornene-2-carboxylic acid,2-trifluoromethyl-5-norbornene-2-carboxylic acid,carboxytetracyclo[4.4.0.1^(2,5).1^(7,10)]dodecyl methacrylate or thelike is substituted can be cited.

The acid stable repeating unit (D) not having a polar group such as ahydroxyl group can be introduced by copolymerizing a monomer that has anacid stable substituent group that does not contain a polar group.Examples of such a compound include aromatic compounds such as styrene,α-methyl styrene, p-methyl styrene, indene or the like; and estercompounds where a carboxyl group of carboxylic acids having an ethylenicdouble bond such as acrylic acid, methacrylic acid, maleic acid, fumaricacid, α-trifluoromethyl acrylic acid, 5-norbornene-2-carboxylic acid,2-trifluoromethyl-5-norbornene-2-carboxylic acid,carboxytetracyclo[4.4.0.1^(2,5).1^(7,10)]dodecyl methacrylate and so onis substituted by a saturated hydrocarbon group having 1 to 20 carbonatoms such as a methyl group, an ethyl group, an iso-propyl group, acyclopentyl group, a cyclohexyl group, a 1-ethyl-1-cyclohexyl group, a2-methyl-2-adamantyl group, a 2-ethyl-2-adamantyl group, a2-propyl-2-adamantyl group, a 2-(1-adamantyl)-2-propyl group, a8-methyl-8-tricyclo[5.2.1.0^(2,6)]decanyl group, a8-ethyl-8-tricyclo[5.2.1.0^(2,6)]decanyl group, a8-methyl-8-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodecanyl group, a8-ethyl-8-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodecanyl group and thelike.

The copolymer according to the invention includes the repeating units(A) and (B) indispensably and, as needs arise, (C) and (D) and mayinclude at least one kind or tow kinds of each of these. A compositionratio of each of the respective repeating units in an obtained resistpolymer can be selected within a range that does not disturb thefundamental performance thereof. That is, in general, a compositionratio of the repeating unit (A) is preferably in the range of 10 to 90mole percent and more preferably in the range of 10 to 80 mole percent.Furthermore, a composition ratio of the repeating unit (B) is preferablyin the range of 10 to 70 mole percent and more preferably in the rangeof 10 to 60 mole percent. A composition ratio of the repeating unit (C)is preferably in the range of 0 to 70 mole percent and more preferablyin the range of 0 to 60 mole percent. A composition ratio of therepeating unit (D) is preferably in the range of 0 to 40 mole percentand more preferably in the range of 0 to 30 mole percent.

When the copolymer for semiconductor lithography of the invention isused as an underlayer film of a multilayer resist, a repeating unit (A′)for improving the adhesiveness with a semiconductor substrate and forreacting with a compound having a bifunctional or more reactive group tocrosslink and a repeating unit (B′) for controlling the solubility to alithography organic solvent are necessarily contained. As the repeatingunit (A′), the repeating unit (A) can be preferably used and, as therepeating unit (B′), the repeating unit (D) can be preferably used.Furthermore, a copolymer for an underlayer film of the multilayer resistmay include the repeating unit (B) and/or (C). When the copolymer forsemiconductor lithography is used as an anti-reflection film, astructure that absorbs radiation irradiated in the lithography processis necessarily included in the repeating unit (A) and/or (D).

The structure that absorbs the radiation differs depending on awavelength of the radiation used. For instance, a naphthalene skeletonor anthracene skeleton is preferable for KrF excimer laser and a benzeneskeleton is preferable for ArF laser. Examples of a polymerizablecompound that imparts a repeating unit having the structure includestyrenes such as styrene, α-methylstyrene, p-methylstyrene,p-hydroxystyrene, m-hydroxystyrene and so on derivatives thereof; andaromatic group-containing esters having an ethylenic double bond such assubstituted or unsubstituted phenyl (meth)acrylate, substituted orunsubstituted naphthalene (meth)acrylate, substituted or unsubstitutedanthracene methyl (meth)acrylate and so on. The repeating unit having astructure that absorbs radiation, depending on the presence of a polargroup, may be contained in either one of the repeating unit (A) or (D)or in both thereof. A composition ratio of the repeating unit having astructure that absorbs radiation is preferably selected in the range of10 to 100 mole percent.

A copolymer for semiconductor lithography of the invention is acopolymer obtained by copolymerizing the above-exemplified monomerhaving a hydroxyl group and a monomer having no hydroxyl group, in whicha molar composition of a hydroxyl group-containing repeating unit in alow molecular weight region corresponding to an area of 5% of acopolymer total peak obtained by gel permeation chromatography (GPC) iswithin ±10% of an average molar composition of the hydroxylgroup-containing repeating unit in a whole of the copolymer. That is,with an average molar composition as a %, the molar composition falls inthe range of 0.90 a to 1.10 a. When the molar composition is higher thanthe range, since a component that is too high in the solubility to analkali developer is present together, a top shape of a pattern isrounded. On the contrary, when the molar composition is lower than therange, since a component that is too low in the solubility to an alkalideveloper is present together, a top shape is angulated or becomescoarser to be incapable of obtaining a pattern high in therectangularity. That is, a demand for miniaturization of the patterncannot be satisfied.

Here, a composition of the hydroxyl group-containing repeating unit in amolecular weight direction can be obtained by subjecting a solutionseparated by the GPC to infrared spectroscopy (IR), nuclear magneticresonance (NMR) or the like to analyze. However, preferably, after asolution separated by the GPC is sprayed on a rotating disc and dried,with the disc rotating, FT-IR is applied, and thereby, a composition ina molecular weight direction can be analyzed in detail. An averagecomposition of the hydroxyl group-containing repeating unit can beanalyzed by means of the IR, NMR and so on. However, preferably, ¹³C-NMRcan be applied to obtain more accurate information.

A producing method of the invention of a copolymer is not particularlyrestricted, as far as it can produce a copolymer where a molecomposition of a hydroxyl group-containing repeating unit in a lowmolecular weight region corresponding to an area of 5% of a copolymertotal peak obtained in the GPC is within ±10% of an average molarcomposition of the hydroxyl group-containing repeating unit in a wholeof the copolymer. However, in order to readily produce the copolymerlike this, a method described below can be preferably applied toproduce.

In the beginning, as a method of polymerizing a copolymer of theinvention, it is preferable that, in the presence of a polymerizationsolvent, by use of a polymerization initiator, at least two kinds ofpolymerizable compounds selected from above-described monomer groups areradical polymerized to obtain.

A polymerization initiator used in a polymerization reaction is notparticularly restricted, as far as it can be generally used as a radicalgenerator. For instance, azo compounds such as 2,2′-azobisisobutylonitrile, 2,2′-azobis(2-methylbutylonitrile), 2,2′-azobisisobutyric aciddimethyl, 1,1′-azobis(cyclohexanone-1-carbonitrile),4,4′-azobis(4-cyanovaleric acid) and so on; and organic peroxidecompounds such as decanoyl peroxide, lauroyl peroxide, benzoyl peroxide,bis(3,5,5-trimethylhexanoyl)peroxide, succinic peroxide,tert-butylperoxy-2-ethylhexanoate and so on can be used singularly or ina combination thereof.

Other than the above, a thiol compound can be used as a chain transferagent. As such thiol compounds, known thiol compounds such as dodecylmercaptan, mercaptoethanol, mercaptopropanol, mercaptoacetic acid,mercaptopropionic acid,4,4-bis(trifluoromethyl)-4-hydroxy-1-mercaptobutane and so on can beused singularly or in a combination thereof.

Usage amounts of the polymerization initiator and the chain transferagent are different depending on producing conditions such as kinds of araw material monomer, a polymerization initiator and a chain transferagent that are used in a polymerization reaction, a polymerizationtemperature, a polymerization solvent, a polymerization method, arefining condition and so on. Accordingly, the usage amounts cannot bespecified in a clear-cut manner, but optimum amounts for obtaining adesired molecular weight are used. In general, when a weight-averagemolecular weight of a copolymer is too high, the solubility to a solventthat is used during the formation of a film and an alkali developerbecomes low; on the other hand, when a weight-average molecular weightis too low, film properties are deteriorated. Accordingly, theweight-average molecular weight is preferably controlled so as to be inthe range of 2,000 to 40,000 and more preferably so as to be in therange of 3,000 to 30,000.

As a method of a polymerization reaction, a so-called batchpolymerization method where all monomers, a polymerization initiator,and, as needs arise, a chain transfer agent are dissolved in apolymerization solvent and heated to a polymerization temperature; aninitiator addition method where, after monomers are dissolved in asolvent and heated to a polymerization temperature, a polymerizationinitiator is added; and a dropwise addition polymerization method wheremonomers, a polymerization initiator and a chain transfer agent arepartially or all mixed or independently dropped in a polymerizationsystem heated to a polymerization temperature can be applied. Amongthese, the dropwise addition method is preferable to make differencesbetween lots smaller, and, in particular, in viewpoint of stablyretaining undropped monomer during dropping, a method where monomers anda polymerization initiator are separately retained and dropped ispreferable.

The solvent that is used in the polymerization reaction is notparticularly restricted, as far as it can stably dissolve raw materialmonomers, an obtained copolymer, a polymerization initiator and a chaintransfer agent. Specific examples of the polymerization solvent includeketones such as acetone, methyl ethyl ketone, methyl amyl ketone,cyclohexanone and so on; ethers such as tetrahydrofuran, dioxane, glyme,propylene glycol monomethyl ether and so on; esters such as ethylacetate, ethyl lactate and so on; ether esters such as propylene glycolmethyl ether acetate and so on; and lactones such as γ-butyrolactone.These can be used singularly or in a combination thereof. A usage amountof the polymerization solvent is not particularly restricted. However,the usage amount thereof is, to one part by weight of the monomer,normally in the range of 0.5 to 20 parts by weight and preferably in therange of 1 to 10 parts by weight. When the usage amount of the solventis too small, in some cases, the monomer precipitates or the viscositybecomes too high to be incapable of maintaining a polymerization systemhomogeneous. On the contrary, when the usage amount of the solvent istoo much, in some cases, the conversion rate of the monomer becomesinsufficient or a molecular weight of the copolymer cannot be heightenedto a desired value.

A polymerization reaction condition is not particularly restricted. Ingeneral, a reaction temperature is preferably in the range ofsubstantially 40 to 100° C. In order to make differences of a copolymerbetween lots of the copolymer smaller, a polymerization temperature isnecessarily controlled severely, that is, preferably controlled within asetting temperature ±1° C. As to a reaction time, in the case of thedropwise addition polymerization, since when a dropping time is longer,a monomer composition and concentration and a radical concentration inthe system can be maintained constant, a composition and a molecularweight of a polymer generated during dropping preferably tend to behomogeneous. On the other hand, a longer dropping time unfavorablylowers the production efficiency per unit hour and disturbs thestability of the monomer during dropping. Accordingly, the dropping timeis selected between 0.5 to 20 hr and preferably between 1 to 10 hrs.After the dropping comes to completion, since unreacted monomer remains,for a constant time, a polymerization temperature is preferablymaintained to age. An aging time is less than 8 hrs and preferablyselected between 1 to 6 hrs. In the case of the batch polymerization, anaging time after a polymerization temperature is attained is selectedbetween 1 to 24 hrs and preferably between 2 to 12 hrs.

Since a copolymer obtained by polymerization contains low molecularweight impurities such as an unreacted monomer, oligomer, polymerizationinitiator and chain transfer agent and reaction byproducts thereof,these have to be removed by refining. Specifically, a polymerizationreaction solution, after as needs arise adding a good solvent to dilute,is brought into contact with a poor solvent to precipitate the copolymeras a solid, and thereby the impurities are extracted in a poor solventphase (hereinafter, referred to as “reprecipitation”) or apolymerization reaction solution is rendered liquid-liquid two-phases toextract the impurities in a solvent phase. When the reprecipitation isconducted, further purification can be applied by a step where after theprecipitated solid is separated from the solvent by filtration,decantation or the like, the resulting solid is redissolved by a goodsolvent, followed by further adding a poor solvent thereto toreprecipitate, or by a step where the precipitated solid is washed witha poor solvent or a solvent mixture of poor solvent and good solvent.When the liquid-liquid two-phase separation is conducted, furtherprecipitation can be applied by separating the poor solvent phase byphase separation, followed by adding a poor solvent or a solvent mixtureof poor solvent and good solvent to the obtained copolymer solution toreprecipitate or separate in liquid-liquid two-phase. These operationsmay be conducted by repeating the same operation or by combiningdifferent operations.

In the refining step, the copolymer and the impurities are separated byuse of the difference of the solubility to the solvent. However, since alow molecular weight region of the copolymer is small in the differenceof the solubility particularly from the impurities, the low molecularweight region is partially extracted together with the impurities. Inparticular, in the case of a copolymer for semiconductor lithography,which is obtained by copolymerizing a plurality of monomers different inthe polarity, depending on the polarity of the poor solvent, acomposition of an extracted low molecular weight copolymer is different.That is, when a polar poor solvent is used, a low molecular weightcopolymer high in a high polarity repeating unit composition isextracted, and, when a nonpolar poor solvent is used, a low molecularweight copolymer high in a low polarity repeating unit composition isextracted.

Accordingly, a method of producing a copolymer for semiconductorlithography, which is a copolymer according to the invention andobtained by copolymerizing a monomer having a hydroxyl group and amonomer having no hydroxyl group and where a molar composition of ahydroxyl group-containing repeating unit in a low molecular weightregion corresponding to an area of 5% of a copolymer total peak in theGPC is within ±10% of an average molar composition of the hydroxylgroup-containing repeating unit in a whole of the copolymer preferablyincludes a step of bringing a copolymer obtained by polymerizing intocontact with a polar solvent having a hydroxyl group to reprecipitate orwash; and a step of bringing the obtained copolymer into contact with anonpolar solvent having no hydroxyl group to reprecipitate or wash. Whenthe step of bringing into contact with a polar solvent having a hydroxylgroup is applied singularly, a composition of the hydroxylgroup-containing repeating unit in a low molecular weight region becomesunfavorably low and, on the other hand, when the step of bringing intocontact with a polar solvent having no hydroxyl group is appliedsingularly, a composition of the hydroxyl group-containing repeatingunit in a low molecular weight region becomes unfavorably high.

In the invention, typical examples of a polar solvent having a hydroxylgroup include compounds having an alcoholic hydroxyl group such aswater, methanol, ethanol, isopropanol, ethylene glycol, ethyl lactateand so on and typical examples of a nonpolar solvent having no hydroxylgroup include linear, branched and alicyclic hydrocarbons such aspentane, n-hexane, iso-hexane, n-heptane, cyclopentane, methylcyclohexane and soon; or aromatic hydrocarbons such as toluene, xyleneand so on. These solvents can be used singularly or in a mixturethereof. Furthermore, the polymerization solvents and solventsexemplified in the coating film forming solvent described below can bemixed and used as well.

A kind and an amount of the poor solvent (polar solvent having ahydroxyl group and nonpolar solvent having no hydroxyl group) used inthe refining are not particularly restricted, as far as a copolymer canbe separated from low molecular weight impurities. However, the kind andamount of the poor solvent can be appropriately selected correspondingto the solubility to the poor solvent of the copolymer, a kind and anamount of a solvent used to polymerize, a kind and an amount of theimpurity and so on. An amount of the poor solvent is generally, to atotal amount of a polymerization reaction solution diluted with a goodsolvent as needs arise, in the range of 0.5 to 50 times, preferably inthe range of 1 to 20 times and more preferably in the range of 2 to 10times. In all cases, when a usage amount of the solvent is less,impurities such as the unreacted monomer, polymerization initiator,chain transfer agent and reaction byproducts thereof can beinsufficiently separated. On the contrary, when the usage amount of thesolvent is too much, the waste liquid increases to cause inconveniencefrom the viewpoint of the workability and the cost.

A temperature of a refining step largely affects on a molecular weightand a molecular weight distribution of a lithography copolymer, theremoval rates of the impurities such as residual monomers and theinitiator residue and various characteristics in the lithographyprocess; accordingly, the temperature has to be rigidly controlled. Whenthe temperature of the refining step is too low, since the solubility ofthe impurities to a reprecipitation solvent and a washing solventbecomes insufficient, the impurities are insufficiently removed to beinefficient. On the other hand, when the temperature of the refiningstep is too high, since the copolymer is eluted in the reprecipitationsolvent and the washing solvent, a composition balance in the lowmolecular weight region of the copolymer may collapse or the yield isunfavorably deteriorated. Accordingly, the refining step is carried outat a temperature in the range of 0 to 40° C. and preferably in the rangeof 0 to 30° C.

Thus refined copolymer can be taken out as powder after drying or as asolution by charging in a good solvent before or after drying toredissolve. As a good solvent that is used to redissolve, ones cited asthe polymerization solvent can be similarly used. A redissolved solutionis preferably passed through a filter having an average pore diameterpreferably of 0.5 μm or less and more preferably of 0.1 μm or less toremove minute solid content, insoluble foreign matters or metals, or thelike.

The refined copolymer solution can be finished into a coating filmforming solution by further distilling away other solvents used in therefining step under reduced pressure while supplying a coating filmforming solvent. As a solvent for forming a coating film is notparticularly restricted. However, normally, the solvent for forming acoating film is selected by taking a boiling temperature, an effect on asemiconductor substrate or other coating films and absorption ofradiation used in the lithography into consideration. Examples of thesolvent generally used to form a coating film include solvents such aspropylene glycol methyl ether acetate, ethyl lactate, propylene glycolmonomethyl ether, methyl amyl ketone, γ-butyrolactone, cyclohexanone andsoon. A usage amount of the solvent is not particularly restricted andis normally in the range of 1 to 20 parts by weight to one part byweight of the copolymer.

When a copolymer is used in a resist, to the coating film formingsolution, a radiation-sensitive acid generator and an acid diffusioninhibitor such as a nitrogen-containing compound or the like, whichinhibits acid from diffusing into a portion that has not been exposed toradiation can be further added to complete a resist composition. As theradiation-sensitive acid generator, ones that are generally used asresist raw materials such as an onium salt compound, a sulfone compound,a sulfone acid ester compound, a sulfone imide compound, adisulfonyldiazomethane compound and so on can be used. Furthermore, tothe resist composition, as needs arise, compounds used to be used asresist additives such as a dissolution inhibitor, a sensitizer, a dyeand so on can be further added. A blending ratio of each of thecomponents (excluding the resist solvent) in the resist composition is,though not particularly restricted, generally selected in the range of 5to 50 mass percent for the polymer concentration, in the range of 0.1 to10 mass percent for the radiation-sensitive acid generator and in therange of 0.001 to 10 mass percent for the acid diffusion inhibitor.

Furthermore, when the obtained copolymer is used as an antireflectionfilm, the polymer is used singularly or blended with bifunctional ormore isocyanate, amine, epoxide or the like capable of crosslinkingbetween polymers.

EXAMPLE

In what follows, the invention will be detailed with reference toexamples. However, the invention is not restricted to the examples. Anaverage copolymer composition (average molar composition of a repeatingunit) of the obtained copolymer was obtained from a measurement of¹³C-NMR. Furthermore, a weight average molecular weight Mw, a degree ofdispersion Mw/Mn and a residual monomer concentration were obtained frommeasurements by gel permeation chromatography (GPC). A copolymercomposition in each of the molecular weights (molar composition of arepeating unit) was obtained by GPC-IR. A pattern evaluation of theobtained copolymer was carried out with a 248 nm exposing device.

(1) Average Copolymer Composition of Copolymer

Into 20 parts by weight of heavy acetone, 10 parts by weight of acopolymer and one parts by weight of chromium (III) acetylacetonate weredissolved to prepare a sample solution. The sample solution was chargedin an NMR tube followed by analyzing by ¹³C-NMR (at 400 MHz,manufactured by Bruker).

(2) Mw and Mw/Mn of Copolymer

In 100 parts by weight of tetrahydrofuran (hereinafter, referred to asTHF), 4 parts by weight of the copolymer were dissolved to prepare asample solution. In a GPC unit (trade name: GPC8220, manufactured byTosoh Corporation) with GPC columns (trade name: KF-804L×4, manufacturedby SHOWA DENKO KK), 20 μL of the sample solution was charged with THF asan elution solution, and an eluted solution was detected with adifferential refractive index (RI) detector. The Mw and Mw/Mn werecalculated based on a calibration curve prepared in advance withstandard polystyrene.

(3) Copolymer Composition in Low Molecular Weight Region Correspondingto 5% of Copolymer Peak in GPC

In a GPC unit (trade name: GPC8220, manufactured by Tosoh Corporation)with GPC columns (trade name: KF-804L×4, manufactured by SHOWA DENKOKK), 150 μL of the sample solution prepared in (2) was charged with THFas an elution solution, and an eluted solution was introduced in aLC-Transform Model 410 (trade name, manufactured by Lab Connections)and, under heating at 110° C., sprayed onto a germanium disc rotating ata constant speed. The disc was set to a rotating stage of a FT-IRoptical module and, by use of FT-IR (trade name, manufactured by JEOL.Ltd.), while rotating the disc, infrared absorption of the copolymercoated on the disc was measured at 100 points. Based on the results andthe ¹³C-NMR analysis results, a composition of a hydroxylgroup-containing repeating unit in a low molecular weight regioncorresponding to 5% of a copolymer peak in GPC was obtained. In whatfollows, examples of calculations are shown. Without restricting toexamples below, of other copolymers as well, a composition of a hydroxylgroup-containing repeating unit in a low molecular weight regioncorresponding to 5% of a copolymer peak in GPC can be obtained.

Calculation Example 1 Hydroxystyrene-Alkyl Acrylate Copolymer

With a hydroxystyrene composition obtained by ¹³C-NMR as N_(OH)(%), analkylacrylate composition as N_(E), peak areas of a hydroxyl group and acarbonyl group of acrylic acid ester in a FT-IR analysis at each ofrespective points of a region corresponding to the copolymer as A_(OH)and A_(E), and sum totals of all points of a region corresponding to thecopolymer as ΣA_(OH) and ΣA_(E), a repeating unit concentration(expressed as C_(OH)) derived from hydroxystyrene in each of the points,a repeating unit concentration (expressed as C_(E)) derived from alkylacrylate, and a copolymer concentration (expressed as C_(P)) can becalculated by formulas below.C _(OH) =N _(OH)×(A _(OH) /

A _(OH)) (%)  (Formula 1)C _(E) =N _(E)×(A _(E) /

A _(E)) (%)C _(P) =C _(OH) +C _(E)(%)

When a low molecular weight region corresponding to 5% of a copolymerpeak in GPC is set up to a point where a total of C_(P) from the lowestmolecular weight of the copolymer is 5% to a point where a sum total ofC_(P)s of all points in a region corresponding to the copolymer and aconcentration of the hydroxyl group-containing repeating unit and acopolymer concentration in the region, respectively, are expressed withΣ_(5%)C_(OH) and Σ_(5%)C_(P), difference (expressed with D_(OH)) betweenthe low molecular weight region of the hydroxyl group-containingrepeating unit and an average composition is calculated by a formulabelow.D _(OH)=[{(Σ_(5%) C _(OH)/Σ_(5%) C _(P))/N _(OH)}−1]×100(%)  (Formula 2)

Calculation Example 2 Hydroxyl Group-ContainingAcrylate-Lactone-Containing Acrylate-Alkyl Acrylate Copolymer

When a hydroxyl group-containing acrylate composition obtained by¹³C-NMR is expressed with N_(OH) (%), peak areas of a hydroxyl group anda carbonyl group of acrylic ester in a FT-IR analysis at each of pointsof a region corresponding to a copolymer, respectively, are expressedwith A_(OH) and A_(E) and sum totals of all points of a regioncorresponding to the copolymer, respectively, are expressed with ΣA_(OH)and ΣA_(E), a concentration of the hydroxyl group-containing acrylate(expressed with C_(OH)) and a copolymer concentration (expressed withC_(P)) at each of points are calculated by formulas below.C _(OH) =N _(OH)×(A _(OH) /ΣA _(OH)) (%)C _(P) =A _(E) /ΣA _(E) (%)  (Formula 3)

When a low molecular weight region corresponding to 5% of a copolymerpeak in GPC is set up to a point where a total of C_(P) from the lowestmolecular weight of the copolymer is 5% to a sum total of C_(P)s of allpoints in a region corresponding to the copolymer and a concentration ofthe hydroxyl group-containing repeating unit and a copolymerconcentration in the region, respectively, are expressed withΣ_(5%)C_(OH) and Σ_(5%)C_(P), difference (expressed with D_(OH)) betweenthe low molecular weight region of the hydroxyl group-containingrepeating unit and an average composition is calculated by a formulabelow.D _(OH)=[{(Σ_(5%) C _(OH)/Σ_(5%) C _(P))/N _(OH)}−1]×100(%)  (Formula 4)

(4) Evaluation of Resist Pattern

To a 15% by weight PGMEA solution that includes 60 parts by weight of acopolymer and 360 parts by weight of PGMEA, 1.0 parts by weight oftrifluoromethanesulfonic acid triphenylsulfonium as a photoacidgenerator and 0.1 parts by weight of triethanolamine were added anddissolved, followed by filtering with a 0.05 μm membrane filter, andthereby a resist composition was prepared. The resist composition wasspin coated on a Si wafer, dried on a hotplate at 120° C. for 90 sec,and thereby a resist thin film having a film thickness of 500 μm wasprepared. The resist thin film was exposed with a KrF excimer laserstepper (NA=0.6, manufactured by Nikon Corporation), immediatelythereafter followed by baking at 120° C. for 90 sec, further followed bydeveloping with a 2.38% by weight tetramethylammonium hydroxide aqueoussolution at room temperature for 60 sec, still further followed byrinsing with pure water to obtain a resist pattern. An optimum exposureamount for obtaining a 200 nm line and space pattern (1:1) was obtainedand this was taken as the optimum exposure amount. Furthermore, apattern shape at that time was observed with a scanning electronmicroscope (SEM). The sensitivity and observation results of patternshapes are summarized in Table 1.

Example 1

In a monomer solution preparation tank maintained in a nitrogenatmosphere, 158 kg of a p-ethylphenol solution containing 24% ofp-hydroxystyrene (hereinafter referred to as “PHS”), 23% of methanol and10% of water, 19.0 kg of tert-butyl acrylate and 1.5 kg of AIBN werecharged and dissolved, thereby a monomer solution was prepared. To apolymerization tank, 35 kg of the monomer solution was transferred,followed by heating to 80° C. under stirring, further followed byfeeding a remaining monomer solution into the polymerization tank keptat 80° C. over 2 hrs to polymerize. After the completion of the feeding,the monomer solution was aged for 2 hrs with a polymerizationtemperature kept at 80° C., followed by cooled to room temperature. Theobtained polymerization solution was dropped in 620 kg of toluene toprecipitate a polymer, followed by removing a supernatant solution. Inthe next place, the polymer was dissolved with 36 kg of methanol,followed by reprecipitating in 620 kg of toluene, further followed twiceby removing a supernatant solution, followed by redissolving in 90 kg ofmethanol. Furthermore, 55 kg of water was added to reprecipitate,followed by removing a supernatant solution, further followed twice byredissolving in 90 kg of methanol, and an obtained methanol solution waspassed through a filter 40QSH (trade name, manufactured by CunoIncorporated). A filtered methanol solution is partially sampled anddried in a reduced pressure dryer, and an obtained pale yellow solid wasanalyzed with ¹³C-NMR and GPC-IR to obtain an average composition, Mwand Mw/Mn of a copolymer and a copolymer composition in a low molecularweight region corresponding to 5% of a copolymer peak. Furthermore, witha remaining methanol solution heating under reduced pressure to driveaway a low boiling temperature solvent such as methanol, propyleneglycol methyl ether acetate (hereinafter referred to as “PGMEA”) wascharged, and thereby a PGMEA solution containing 15% of the copolymerwas prepared. Thereafter, according to a method described in the (4), aresist composition was prepared, followed by evaluating a resistpattern. Results are shown in Table 1.

Example 2

Except that, in place of 19.0 kg of tert-butyl acrylate and 1.5 kg ofAIBN in example 1, 20.5 kg of 1-ethyl-1-cyclopentyl acrylate and 2.2 kgof AIBN were used, similarly to example 1, a copolymer was obtained, andan average composition, Mw and Mw/Mn of a copolymer and a copolymercomposition in a low molecular weight region corresponding to 5% of acopolymer peak were analyzed and a resist pattern was evaluated. Resultsare shown in Table 1.

Example 3

In a raw material preparation tank maintained in a nitrogen atmosphere,63.0 kg of methyl ethyl ketone (hereinafter, referred to as “MEK”), 15.6kg of 5-methacryloyloxy-2,6-norbornane carbolactone (hereinafter,referred to as “NLM”), 17.8 kg of 2-methyl-2-adamantyl methacrylate(hereinafter, referred to as “MAM”) and 8.1 kg of 3-hydroxy-1-adamantylmethacrylate (hereinafter, referred to as “HAM”) were charged andstirred to dissolve at a temperature in the range of 20 to 25° C.,thereby a monomer solution was prepared. Furthermore, in a separate tankkept in a nitrogen atmosphere, 10.0 kg of MEK and 1.0 kg ofdimethyl-2,2′-azobisisobutyrate were charged, followed by stirring at atemperature in the range of 10 to 20° C. to dissolve, and thereby aninitiator solution was prepared. In a polymerization tank kept in anitrogen atmosphere, after 24.0 kg of MEK was charged and heated to 80°C. under stirring, the initiator solution kept at room temperature (ca20° C.) and the monomer solution heated in the range of 25 to 30° C.,respectively, were simultaneously began to feed in a polymerization tankkept at 80° C. and fed at constant speeds over 4 hrs. After completionof the feeding, the polymerization temperature was kept at 80° C. to agefor 2 hrs, followed by cooling to room temperature, and a polymerizationsolution was taken out. An obtained polymerization solution was droppedin 420 kg of n-hexane to precipitate a polymer, followed by filtering,and an obtained wet cake was twice repeated to wash with 350 kg ofmethanol containing 5% by weight of water and filter. The obtained wetcake was partially sampled and dried in a reduced-pressure dryer, and anobtained white powder was analyzed by ¹³C-NMR and GPC-IR to obtain anaverage composition, Mw and Mw/Mn of the copolymer and a copolymercomposition in a low molecular weight region corresponding to 5% of acopolymer peak. A remaining wet cake was redissolved in MEK and filteredwith a filter 40QSH (trade name, manufactured by Cuno Incorporated),followed by charging PGMEA while driving away MEK by heating underreduced pressure, and thereby a PGMEA solution containing 15% of thecopolymer was prepared. Thereafter, similarly to example 1, a resistpattern was evaluated. Results are shown in Table 1.

Example 4

In a raw material preparation tank maintained in a nitrogen atmosphere,61.0 kg of MEK, 13.3 kg of α-methacryloyloxy-γ-butyrolactone(hereinafter referred to as “GBLM”), 19.7 kg of MAM and 9.0 kg of HAMwere charged and stirred at a temperature in the range of 20 to 25° C.,thereby a monomer solution was prepared. Furthermore, in a separate tankkept in a nitrogen atmosphere, 11.0 kg of MEK and 1.1 kg of AIBN werecharged, followed by stirring at a temperature in the range of 10 to 20°C. to dissolve, and thereby an initiator solution was prepared. In apolymerization tank maintained in a nitrogen atmosphere, 25.0 kg of MEKwas charged. Operations after that were carried out similarly to example3, an average composition, Mw and Mw/Mn of a copolymer and a copolymercomposition in a low molecular weight region corresponding to 5% of acopolymer peak were analyzed and a resist pattern was evaluated. Resultsare shown in Table 1.

Comparative Example 1

Except that in place of, after 55 kg of water is added to reprecipitateand a supernatant solution is discarded, an operation of redissolvingwith 90 kg of methanol being repeated twice, 540 kg of n-hexane wasadded to reprecipitate and a supernatant solution was discarded,followed by once redissolving with 90 kg of methanol, operations otherthan the above were carried out similarly to example 1, and an averagecomposition, Mw and Mw/Mn of a copolymer and a copolymer composition ina low molecular weight region corresponding to 5% of a copolymer peakwere analyzed and a resist pattern was evaluated. Results are shown inTable 1.

Comparative Example 2

Except that in place of, after 55 kg of water is added to reprecipitateand a supernatant solution is discarded, an operation of redissolvingwith 90 kg of methanol being repeated twice, 540 kg of n-hexane wasadded to reprecipitate and a supernatant solution was discarded,followed by once redissolving with 90 kg of methanol, operations otherthan the above were carried out similarly to example 2, and an averagecomposition, Mw and Mw/Mn of a copolymer and a copolymer composition ina low molecular weight region corresponding to 5% of a copolymer peakwere analyzed and a resist pattern was evaluated. Results are shown inTable 1.

Comparative Example 3

Except that a polymerization solution was dropped not in 420 kg ofn-hexane but in 700 kg of methanol containing 5% by weight of water,operations other than that were carried out similarly to example 3, andan average composition, Mw and Mw/Mn of a copolymer and a copolymercomposition in a low molecular weight region corresponding to 5% of acopolymer peak were analyzed and a resist pattern was evaluated. Resultsare shown in Table 1.

Comparative Example 4

The same process as that described in Example 4 was carried out exceptthat a polymerization solution was dropped not in 420 kg of n-hexane butin 700 kg of methanol containing 5% by weight of water, and an averagecomposition, Mw and Mw/Mn of a copolymer and a copolymer composition ina low molecular weight region corresponding to 5% of a copolymer peakwere analyzed and a resist pattern was evaluated. Results are shown inTable 1.

PHS HAM NLM GBLM TBA ECPA MAM Composition Composition CompositionComposition Composition Composition Composition (mole %) (mole %) (mole%) (mole %) (mole %) (mole %) (mole %) Example 65.4 34.6 Example 69.930.1 Example 20.8 39.7 39.5 Example 20.3 39.7 40.0 Comparat 66.8 33.2Comparat 71.0 29.0 Camparat 20.2 39.9 39.9 Comparat 19.8 39.8 40.4Average 5% area OH OH Sensitivity Pattern composition compositionDeviation Mw × 10³ PD mJ/cm² Shape (mole %) (mole %) (%) Example 20.31.99 45 Excellent 65.4 70.3 7.5% Example 14.9 1.77 40 Excellent 69.972.4 3.6% Example 10.2 1.89 43 Excellent 20.8 21.8 5.0% Example 10.31.84 41 Excellent 20.3 21.7 6.9% Comparat 19.7 2.05 43 R-top 66.8 78.417.4% Comparat 14.5 1.82 39 R-top 71.0 80.2 13.0% Camparat 10.4 1.86 45T-top 20.2 17.0 −15.5% Comparat 10.5 1.81 421 T-top 19.8 16.4 −16.9% Inthe table, R-top means that a top shape of a pattern is rounded andT-top means that a top shape of a pattern angulated in T-shape.

1. A copolymer for semiconductor lithography produced by a processcomprising: copolymerizing a monomer having a hydroxyl group and amonomer having no hydroxyl group in a polymerization reaction solutioncomprising a polymerization solvent to produce the copolymer; andbringing the copolymer, which is present in the polymerization reactionsolution, into contact with a poor solvent comprising: a polar solventhaving a hydroxyl group; and a nonpolar solvent having no hydroxylgroup, to reprecipitate or wash the copolymer, wherein a ratio of theamount of the poor solvent to a total amount of the polymerizationreaction solution diluted with the polymerization solvent is 1-20:1, andwherein a molar composition of a hydroxyl group-containing repeatingunit in a low molecular weight region corresponding to 5% of a copolymertotal peak by gel permeation chromatography is within ±10% of an averagemolar composition of hydroxyl group-containing repeating units in atotal of the copolymer.
 2. The copolymer for semiconductor lithographyaccording to claim 1, wherein the monomer having a hydroxyl group isselected from the group consisting of a hydroxystyrene, ahydroxyhalogenoalkylstyrene, a carboxylic acid having an ethylenicdouble bond, a hydroxyalkyl ester of carboxylic acid having an ethylenicdouble bond, and a hydroxyhalogenoalkyl ester of carboxylic acid havingan ethylenic double bond.
 3. The copolymer for semiconductor lithographyaccording to claim 1, wherein the monomer having no hydroxyl group is amonomer having a hydroxyl group that is protected with a protectinggroup, wherein the monomer having a hydroxyl group is selected from thegroup consisting of a hydroxystyrene, a hydroxyhalogenoalkylstyrene, acarboxylic acid having an ethylenic double bond, a hydroxyalkyl ester ofcarboxylic acid having an ethylenic double bond, and ahydroxyhalogenoalkyl ester of carboxylic acid having an ethylenic doublebond, and wherein the protecting group is selected from the groupconsisting of a saturated hydrocarbon group having 1-20 carbon atoms andan oxygen-containing hydrocarbon group having 2-24 carbon atoms.
 4. Asemiconductor lithography composition comprising the copolymer forsemiconductor lithography according to claim
 1. 5. A process forproducing a copolymer for semiconductor lithography, wherein saidprocess comprises: copolymerizing a monomer having a hydroxyl group anda monomer having no hydroxyl group in a polymerization reaction solutioncomprising a polymerization solvent to produce the copolymer; andbringing the copolymer, which is present in the polymerization reactionsolution, into contact with a poor solvent comprising: a polar solventhaving a hydroxyl group; and a nonpolar solvent having no hydroxylgroup, to reprecipitate or wash the copolymer, wherein a ratio of theamount of the poor solvent to a total amount of the polymerizationreaction solution diluted with the polymerization solvent is 1-20:1, andwherein a molar composition of a hydroxyl group-containing repeatingunit in a low molecular weight region corresponding to 5% of a copolymertotal peak by gel permeation chromatography is within ±10% of an averagemolar composition of hydroxyl group-containing repeating units in atotal of the copolymer.
 6. The process for producing a copolymer forsemiconductor lithography according to claim 5, wherein the monomerhaving a hydroxyl group is selected from the group consisting of ahydroxystyrene, a hydroxyhalogenoalkylstyrene, a carboxylic acid havingan ethylenic double bond, a hydroxyalkyl ester of carboxylic acid havingan ethylenic double bond, and a hydroxyhalogenoalkyl ester of carboxylicacid having an ethylenic double bond.
 7. The process for producing acopolymer for semiconductor lithography according to claim 5, whereinthe monomer having no hydroxyl group is a monomer having a hydroxylgroup that is protected with a protecting group, wherein the monomerhaving a hydroxyl group is selected from the group consisting of ahydroxystyrene, a hydroxyhalogenoalkylstyrene, a carboxylic acid havingan ethylenic double bond, a hydroxyalkyl ester of carboxylic acid havingan ethylenic double bond, and a hydroxyhalogenoalkyl ester of carboxylicacid having an ethylenic double bond, and wherein the protecting groupis selected from the group consisting of a saturated hydrocarbon grouphaving 1-20 carbon atoms and an oxygen-containing hydrocarbon grouphaving 2-24 carbon atoms.
 8. A semiconductor lithography compositioncomprising the copolymer for semiconductor lithography produced by theprocess according to claim 5.